multimeter jittery in autorange

[teus]

What would cause a multimeter to be very jittery in autorange mode, but completely fine when you set the range yourself?
I opened it, and the inside looks clean. No water damage or corrosion, no swollen electrolytic capacitors.
It's an Appa 205 multimeter. Manufacturer didn't answer my request for a user manual or a service manual.

[Kleinstein]

For testing the noise in the votlage mode, one should have the input shorted and not open. With open input there can be swtiching between ranges, that can effect the noise and for the AC range the time for settling can be quite long ( the AV mode naturally averages over the last second of so with an analog filter). So some of the shown numbers can be still effected from artifacts from range switching.

[teus]

For testing the noise in the votlage mode, one should have the input shorted and not open. With open input there can be swtiching between ranges, that can effect the noise and for the AC range the time for settling can be quite long ( the AV mode naturally averages over the last second of so with an analog filter). So some of the shown numbers can be still effected from artifacts from range switching.

with the input shorted to the ground, the automatic range mode is stable.
it's not about cycling through the different modes quickly, I can wait as long as I want, and the autorange function will constantly cycle through different range settings, or give a reading of 500mv.

[Kleinstein]

The open input will pic up quite some noise and this can make the DMM switch ranges from time to time. The open circuit case is not really relevant for a real measurement. If you have a signal source with such a high impedance to be comparable to the DMM input resistance, the DMM is the wrong instrument. At the very least one still use manual ranging for these rare cases. The higher end bench DMMs usually also have a high impedance (e.g. > 1 Gohms) mode for such cases.